Sampling device and method for monitoring of liquids

ABSTRACT

Methods and devices for measuring chemical or biological properties of a liquid from a subsurface position are disclosed, wherein a closed casing is submerged in the liquid to be sampled. The flow of the liquid for the sampling is driven by a hydrostatic pressure and is thus independent of pumps or the like when placed at the correct subsurface position. The flow rate is in a first aspect of the present invention controlled by providing a constant hydrostatic pressure during the sampling period. Alternatively, the inlet is provided with a cartridge comprising a tracer material, which is partly soluble by the liquid and is released proportional to the flow rate.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods and devices for measuringchemical or biological properties of a liquid from a subsurfaceposition.

BRIEF DISCUSSION OF RELATED ART

The most frequently used method to take liquid samples from, forexample, natural water bodies including groundwater, rivers and lakes isby pumping a certain volume of the liquid into a closed casing. In agroundwater well for example, the common method is to sink a pump intothe groundwater well and pump the groundwater through tubing to a samplecontainer on the surface.

To avoid pumping, so called no-purge samplers have been developed thatsample the water down-hole in the well, thus avoiding the need foractively pumping the water to the surface, for example a device asdisclosed in U.S. Pat. No. 6,481,300. A low-flow sampling well insert isdisclosed in WO 2003/072908 (Learned), in which the flow into a sampletube is allowed after exerting downward pressure on the sample tube. Adisadvantage of this method is that due to the slow rate of sampling,volatile compounds that enter the sampling tube, can volatilize and beremoved again from the sampling tube through the air-outlet.

In a lake or the sea it is also possible to use a method in which thesample casing is lowered to a certain depth and instantaneously filledupon actuators (electronic or other) that allows entrance of thesurrounding water to the casing (e.g. U.S. Pat. No. 3,367,191 Richard).Variations maybe several sampling casings at several depths that areopened simultaneously (e.g. EP 1 521 954, Sauter). After the collectionof these so called grab samples, the casing is usually storedrefrigerated and brought to the laboratory for subsequent analysis ofchemical properties and concentration of solutes. Often measuredparameters measured in the laboratory are plant nutrients, especiallynitrogen and phosphorus, heavy metals, pesticides, and other organiccontaminants.

An important limitation of above described methods is that the obtainedresults represent a concentration value at a fixed period in time.Concentrations of chemicals in water do often vary strongly in time. Inorder to have a representative average concentration over a longerperiod, e.g. months up to one year, it is necessary to obtain severalsamples during this period, which is expensive and time consumingbecause it requires repeated site visits and chemical analyses.

Another problem encountered by the above described methods is that formany chemical parameters it is necessary to refrigerate the obtainedwater samples for conservation purposes before it is analyzed in thelaboratory. Hence, the sample container must be shipped underrefrigerated conditions and the chemical analysis must be performed soonafter the sampling event. Further, it cannot be avoided that the liquidand dissolved chemicals come into physical contact with equipment suchas tubing and sample container. Therefore it is of importance that thesematerials are chosen such that they do not interfere with or adsorb thecompounds to be measured. Also, these materials do have to be very cleanto avoid false positive detects, which is especially important formicro-contaminants that are detected at very low concentration levels.Hence, either disposable equipment—e.g. tubing, flasks—are used, or thesample containers have to be cleaned very thoroughly in between twosamplings. This cleaning process is time- and energy consuming and alsorequires the frequent use of organic solvents.

One way to obtain time-resolved information is by using automatedsamplers that takes a series of samples in time, usually by means of apump that is time-controlled by an electronic device. This pumptransfers the liquid in response to a sensor or following pre-programmedtime intervals into a series of containers, and thereby collects aseries of samples without the user being physically being present at thelocation (see e.g. DE 198 36 292). The water samples can either beanalyzed separately, or they can be mixed such that time-averagedconcentrations can be obtained. However, the conservation problem of thewater sample is still applicable; hence the water samples device shouldpreferably be refrigerated when taking samples over longer time periods.As a consequence, these devices are power-consuming and repetitive sitevisits need to be performed to change battery power supply or the like,so they are less suited for remote locations.

In WO 98/40717 (Fiedler and Davison) is disclosed an improved automatedsampler, where the pump is used to transfer water at a controlled ratethrough a collecting cartridge which is filled with an adsorbent that isselected to adsorb the solutes of interest, a so called solid phaseextraction cartridge. After the device is installed for a certain amountof time, the cartridges are brought to the laboratory, and adsorbedsolutes are extracted from the adsorbent and measured using standardmethods. Because the pump is working at a controlled flow rate, it isalso possible to know the amount of water passing the cartridge, and,hence, backward calculate the average solute concentration during thesampling period. A similar apparatus for time-averaged sampling ofchemicals in groundwater is disclosed in U.S. Pat. No. 4,717,473 (Scottand Russel), in which the pumping unit and sorptive media cartridge areinstalled down-hole in a groundwater well. This method is called on sitesolid phase extraction, the primary advantage being that it eliminatesthe need for the storage of aqueous samples. However, these devicesstill have power consuming pumps and other electronic functions, makingthe sampler expensive and susceptible to servicing.

In WO 03/098167 (de Jonge and Rothenberg) and WO 01/33173 there aredisclosed passive sampling devices that are placed in moving liquids toestimated the flux of the liquid and dissolved solutes. Described areapplication in, among other, groundwater and aquifers. These devicesconsist of porous liquid-permeable units that are in capillary contactwith the surrounding liquid. The permeable units contain adsorbents thatcapture the solids of interest, and tracer compounds that are leachedout of the units in proportion with the volume of the liquid passing thesampler. The technical procedure involves installation of the device inthe medium of interest, allowing passive capillary contact with thesurrounding liquid over a certain time period, removing of the device,and retrieving the accumulated amount of the solute and the remainingamount of the tracer compound. The advantage is that these devices areable to measure both an in-situ flux (mass and momentum movement) of thesolute and the liquid as well as an average concentration (mass pervolume) as opposed to above described methods that only measure soluteconcentrations. Also, these devices do not have power consumingfunctions and therefore do not need to be serviced when installed forlonger periods at remote locations. These methods have the disadvantage,that the optimal length of the installation period is dependent on themagnitude of the fluid momentum flux adjacent to the sampler: the lowerthe flux, the longer it takes to do an accurate flux measurement.Clearly, the magnitude of the flux is normally not known a-priori, asthe objective of the device is to measure the actual flux. Anotherdisadvantage is that these devices are not suited for applications inopen water bodies such as lakes, marine environments, and ponds, as theflow in these environments is either too high, turbulent, or too low tobe accurately measured. As these devices depend on a laminar flowconditions, they can in this case measure neither solute flux nor soluteconcentrations.

Another passive sampling method used a tube and cartridge with sorptivemedia directly installed in a groundwater well (Pankow et al., GroundWater, Vol. 23, no. 6, 1985). The cartridge was connected with thetubing and a flow restrictor, the tubing leading to the surface, and thecartridge lowered down the well; the water column pressed the waterthrough the cartridge containing a sorptive media. The main disadvantagefrom this method is that the flow rate of sampling is not constant overtime, due to the rising water column in the tube, causing a gradualincrease in the back pressure and therewith a decrease in the samplingflow rate. Therefore, the method is less suited to obtain time-averagedconcentrations.

Other documents disclose passive samplers, in which the mass transferfrom the surrounding liquid to the collector occurs through a membranethat is impermeable to the sampled liquid but permeable to theinvestigated solutes (U.S. Pat. No. 5,996,423, WO 92/04646, U.S. Pat.No. 5,904,743, WO 01/14852). Mass transfer through the semi-permeablemembrane is then governed by diffusion, and the mass concentration ofthe solute in the surrounding liquid is calculated using eitherequilibrium values or diffusion parameters. An important feature of themethod is that it measures only the free-dissolved phase, and istherefore often used as a measure for the bio-available fraction. Also,the method these devices can in principle sample solutes over longertime periods. One disadvantage of this method is that the concentrationof the solute in the fluid medium directly adjacent to membrane isdependent on the mixing of the liquid, and hence on the turbulenceand/or flow rate surrounding the membrane (Gustavson, K. E.; Harkin J.M., Environ. Sci. Technol. 2000, 34, 4445-4451). In the absence ofsufficient mixing, the mass transfer through the membrane will becontrolled by the magnitude of the liquid flux in the surrounding fluidmedium, and a direct back-calculation of the concentration withdiffusion parameters is no longer possible. Another disadvantage is thatdiffusion coefficient for each single monitored molecule should becalibrated individually (Huckins et al., Environ. Sci. Technol. 1999,33, 3918-3923). Diffusion parameters can be strongly sensitive totemperature changes. Another disadvantage is that these devices are notpermeable to mobile colloids, that can act of carrier of strongly sorbedcompounds such as phosphorus, heavy metals, apolar contaminants etc.Hence, solutes that are sorbed to suspended colloids are not sampledusing these devices.

Thus, the overall problem to be solved with the known devices is toprovide a method for in-situ sampling of high-precision average chemicalor biological properties of a stagnant or flowing liquid over a longertime period without the need for pumping, vacuum or other powerconsuming functions as well as a device therefore.

This and other problems are solved with the present invention asdescribed in the claims and in the description below.

BRIEF SUMMARY OF THE INVENTION

The method and device of the present invention comprises a closed casingsubmerged in the liquid to be sampled, wherein the above object isreached and a high precision of average properties is obtained. The flowof the liquid for the sampling is driven by a hydrostatic pressure andis thus independent of pumps or the like when placed at the correctsubsurface position, and the flow rate is in a first aspect of thepresent invention controlled by providing a liquid conduit from theinlet for the liquid into the casing and to a position inside the cavityof the casing well above the bottom of the cavity, so that thehydrostatic pressure and thus the flow rate is substantially constantduring the sampling period. Alternatively, the inlet is provided with acartridge comprising a tracer material, which is partly soluble by theliquid and is released proportional to the flow rate. Thus, when thedevice is analyzed after the sampling period, an analysis of theremaining tracer material in the cartridge will reveal the total flow ofthe liquid that has flown into the cavity of the casing. The samplingmay take place over a long period, from days to months, and the amountof liquid within the cavity at the end of the sampling period is lessthan the total flow due to evaporation. Furthermore, the two methods,i.e. the liquid conduit and the tracer material may be combined toprovide a high degree of precision of the average values obtained.

Thus, the present invention relates to a method for determining chemicalor biological properties of a liquid and a device therefore, the methodcomprising the steps of

-   -   situating a sampling device having a fluid-filled cavity at a        subsurface position below the upper surface of the liquid, the        fluid having a density lower than the liquid,    -   allowing a flow of the liquid through an inlet opening of the        sampling device and into the cavity for a sampling period,    -   simultaneous allowing a flow of the fluid out from the cavity        through an outlet opening of the sampling device,    -   removing the sampling device from the subsurface position for        subsequent analysis for determining said chemical or biological        properties of the liquid, wherein the inlet opening of the        sampling device is connected to a liquid conduit having its        outlet inside the cavity and above the bottom of the cavity, so        that the free surface of the liquid inside the cavity during        most of the sampling period, such as at least 80% thereof,        preferably at least 95% thereof, is below the liquid conduit        outlet, for the hydrostatic pressure driving the flow of the        liquid into the cavity to be substantially constant during most        of the sampling period.

The fluid in the cavity at the beginning of the sampling period willnormally be atmospheric air, but may e.g. for sampling in other liquidsthan water, such as oil, be a lighter liquid, such as an alcohol.

Said sampling period is preferably at least one hour, preferably withinthe range of 1 day to 400 days and more preferred within the range of 14days to 200 days. For the design of the device, the volume inside thecavity below the level of the liquid conduit outlet and the liquidinflow rate may be chosen so as to allow for such sampling period.

The liquid inflow rate is in a preferred embodiment of the presentinvention within the range of 0.0001-5 Litres/day, more preferred within0.0005-0.1 Litres/day and even more preferably within 0.001-0.02Litres/day. In order to control the liquid inflow rate, the inlet of thesampling device may be provided with a backpressure regulating device soas to regulate the liquid inflow rate. In a preferred embodiment, thebackpressure regulating device comprises a capillary tubing having aninternal diameter of 10-2000 μm, preferably 10-500 μm and morepreferably 25-150 μm, and the capillary tubing may constitute at least apart of the liquid conduit.

Alternatively, the backpressure regulating device may be constituted byan inlet filter having a nominal filtration porosity of 0.1-2000 μm,preferably 0.5-100 μm, and more preferably 1-20 μm or an in-lineback-pressure regulating restriction valve.

The chemical or biological properties of the sampled liquid may bedetermined from analysis of the content of the cavity. However, this isnot expedient for all types of properties, as the components in theliquid in the cavity may deteriorate over time, e.g. due to evaporationand/or the exposure to atmospheric air. Thus, it may be advantageousthat the inflow passes through a cartridge containing a material thatinteracts with components of the liquid, and said chemical or biologicalproperties of the liquid are determined by a subsequent analysis of thecartridge.

In particular, the cartridge may contain at least one sorbent matrixbeing permeable to and insoluble by the liquid, the matrix comprising amaterial having sorbent properties for components of the liquid beingindicative for the chemical or biological properties thereof to bedetermined. The material may be an organic, inorganic or hybridorganic/inorganic material. In a preferred embodiment, the sorbentmatrix is chosen from the following groups of materials: silica,aluminium silicate, aluminium zirconium, metal oxides, synthetic ionexchange resins, carbonaceous materials, zeolites, carbohydrates andsynthetic polymeric materials.

The cartridge may further as mentioned previously comprise at least onefluid permeable partially soluble tracer material, which is releasedwith controlled rate from the cartridge into fluids to be measured, sothat the total flow trough the cartridge may be determined from analysisof the cartridge. Details about preferred embodiments of the applicationof the tracer material are discussed further below.

In a particular embodiment, the device is equipped with more than onesuch cartridge containing identical and/or different sorbent matricesand/or tracer substances.

The present invention relates in the alternative aspect to a method fordetermining chemical or biological properties of a liquid and a devicetherefore, the method comprising the steps of

-   -   situating a sampling device having a fluid-filled cavity at a        subsurface position below the upper surface of the liquid, the        fluid having a density lower than the liquid,    -   allowing a flow of the liquid through an inlet opening of the        sampling device and into the cavity for a sampling period,    -   simultaneous allowing a flow of the fluid out from the cavity        through an outlet opening of the sampling device,    -   removing the sampling device from the subsurface position for        subsequent analysis for determining said chemical or biological        properties of the liquid,        wherein the inflow passes through a cartridge containing at        least one liquid permeable partially soluble tracer material,        which is released with controlled rate from the cartridge into        fluids to be measured, and a measure for the total liquid flow        through the cartridge is obtained by analysing the remaining        content of tracer material in the cartridge.

The at least one tracer material is in a preferred embodiment chosenfrom the following groups of materials: inorganic, organic and hybridorganic/inorganic salts; organic, inorganic or hybrid organic/inorganicsolids, including polymers, copolymers, block copolymers and oligomersin which hydrolysis of certain bonds can lead to the loss of part of thematerial; and microencapsulated materials.

The tracer material may in particular be a salt having a solubilityproduct (K_(sp)) in the fluid in question of between 10⁻² and 10⁻⁶⁰,preferably between 10⁻² and 10⁻⁴⁰ and more preferably between 10⁻⁵ and10⁻¹².

The tracer material is preferably chosen from the following group ofsalts: CaF₂, Ca-Citrate, CaHPO₄, Ca-oleate and Ca-laurate, which saltshave suitable properties for the purpose.

Furthermore, the cartridge may further contain a material that interactswith components of the liquid, and said chemical or biologicalproperties of the liquid are determined by analysis of the cartridge, inparticular at least one sorbent matrix being permeable to and insolubleby the liquid, the matrix comprising a material having sorbentproperties for components of the liquid being indicative for thechemical or biological properties thereof to be determined. The sorbentmatrix may be made from an organic, inorganic or hybridorganic/inorganic material.

In particular, the sorbent matrix may be chosen from the followinggroups of materials: silica, aluminium silicate, aluminium zirconium,metal oxides, synthetic ion exchange resins, carbonaceous materials,zeolites, carbohydrates and synthetic polymeric materials.

In order to provide a constant inflow of the liquid to the cavity, theinlet opening of the sampling device may be connected to a liquidconduit having its outlet inside the cavity above the bottom of thecavity, so that the free surface of the liquid inside the cavity duringmost of the sampling period is below the liquid conduit outlet for thehydrostatic pressure driving the flow of the liquid into the cavity tobe substantially constant during most of the sampling period. Thepreferred features of such liquid conduit and the possible provision ofa backpressure regulating device are discussed previously.

Said sampling period is preferably at least one hour, preferably withinthe range of 1 day to 400 days and more preferred within the range of 14days to 200 days. For the design of the device, the volume inside thecavity below the level of the liquid conduit outlet and the liquidinflow rate may be chosen so as to allow for such sampling period.

The liquid inflow rate is in a preferred embodiment of the presentinvention within the range of 0.0001-5 Litres/day, more preferred within0.0005-0.1 Litres/day and even more preferably within 0.001-0.02Litres/day. In order to control the liquid inflow rate, the inlet of thesampling device may be provided with a backpressure regulating device soas to regulate the liquid inflow rate. In a preferred embodiment, thebackpressure regulating device comprises a capillary tubing having aninternal diameter of 10-2000 μm, preferably 10-500 μm and morepreferably 25-150 μm, and the capillary tubing may constitute at least apart of the liquid conduit.

Alternatively, the backpressure regulating device may be constituted byan inlet filter having a nominal filtration porosity of 0.1-2000 μm,preferably 0.5-100 μm, and more preferably 1-20 μm or an in-lineback-pressure regulating restriction valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention are illustrated with the encloseddrawings, of which

FIG. 1 shows a first embodiment of a device according to the presentinvention installed at a subsurface position prior to operation (FIG.1A) and during operation (FIG. 1B) of the device,

FIG. 2 shows a second embodiment of a device according to the presentinvention installed at a subsurface position prior to operation (FIG.1A) and during operation (FIG. 1B) of the device,

FIG. 3 shows the installation of the sampling device of FIG. 1 in agroundwater well,

FIG. 4. is a curve showing the linear relationship of sampling flow ratewith depth in the 1-6 m depth interval, and

FIG. 5. is a curve showing the linear relationship of sampling flow ratewith depth in the 0.4-1.7 m depth interval.

The drawings are enclosed for describing preferred embodiments of thepresent invention and are not to be regarded as limiting for the scopeof protection as outlined in the claims.

DETAILED DESCRIPTION OF THE INVENTION

In the figures are shown improved sampling device and methods inaccordance with the present invention for in-situ monitoring ofcontinuously time-averaged concentration values of solutes over longertime periods, say from one day up to a year.

FIG. 1A shows a schematic view of one preferred embodiment of theinvention, having a casing 1 of the device submerged in the liquid 2upon installation. The casing 1 itself may have any desirable shape, butoften a cylindrical shape will be preferred. The casing 1 may beproduced of any desirable material that is water-tight and can withstandthe pressure of the surrounding liquid 2, including but not limited tostainless steel, polyethylene, polypropylene, polytetrafluorethylene,polyoxmethylene, and polyvinyl chloride. Also, the casing 1 itself canbe assembled from several components (not shown in figure). As anexample, a cylinder may be capped with a top and bottom lid, secured tothe cylinder through water tight fittings, e.g., using flexible o-rings.The top and bottom lid contain the inlet 3 and outlet conduits 4.Depending on the volume weight of the casing material, the wallthickness of the casing may be chosen such that weight of the casing ishigher than the weight of the liquid 2 displaced by the casing.Alternatively, if the casing is buoyant in the liquid, it is possible toattach a weight to the casing (not shown). In both cases, the casing canbe installed through a flexible wire at a certain depth without the needof securing the sampler to a fixed point.

The interior cavity 5 of the casing 1 is initially filled withatmospheric air and is in capillary contact with the exterior liquid 2through a capillary tubing 6, inlet conduit 7, and solid phaseextraction cartridge 8. The mode of fitting of the capillary tubing 6and cartridge 8 to the casing 1 and inlet conduit 7 can be any preferredwater-tight fitting. Examples of this fitting include, but are notlimited to, a luer, luer-lock, flat bottom fitted fittings with tightfitting o-rings, and threaded fittings with expandable ferrules. Thesolid phase extraction cartridge 8 contains at least one adsorbent 9.This adsorbent or mix of adsorbents is selected with the view ofadsorbing a certain range of solutes, as described in more detail in WO03/098167. The use of a cartridge 8 with a sorbent media 9 at the inletconduit is especially needed if constituents are to be sampled thatshould not be exposed to air, either because of a risk of volatilizationfrom the casing 1, or because of a risk of chemical or microbiologicaldegradation. The sorption of the constituents is very strong so that thecompounds are chemically and biologically preserved during the samplingperiod.

The cartridge depicted in FIG. 1 also contains at least one tracersubstance 10 that has the function of recording the volume of the waterpassing the cartridge. The tracer substance 10 goes into solution inproportion to the volume passing the cartridge 8, as described in detailin WO 03/098167. The adsorbent 9 and tracer substances 10 are kept inplace with the help of porous filters, called frits (not shown in FIG.1).

Such frits may be produced by any suitable material, including but notlimited to porous glass, porous plastic (such as polyethylene,polytetrafluorethylene, or polyetheretherketon), porous metals (such assteel or titanium) or metal alloys. Besides having the function ofkeeping the adsorbent 9 and tracer materials 10 physically secured inthe cartridge 8, the frits also physically precludes particles largerthan the nominal pore size of the frit to enter the cartridge 8.

An inline filter positioned in between the cartridge 8 and the capillarytubing 6 can be used in order to prevent small particles to enter andpossibly block the capillary tubing 6. The capillary tubing 6 has thefunction of controlling the hydraulic resistance of the liquid path intothe cavity 5 of the casing 1. Capillary flow theory learns that, given acertain pressure head, the flow is proportional with r⁴, with r is theinternal radius of the capillary tubing, and proportional with 1/L, withL is the length of the capillary tubing 6. Hence, the radius and lengthof the capillary tubing 6 can be used to control the flow rate of theliquid into the cavity 5 of the casing 1. In FIG. 1, the capillarytubing 6 is extended vertically into the casing 1, and has its outlet 11near the top of the sample casing 1, so the direction of the liquid 2entering the casing 1 is upward. In order to reach a desired length andhydraulic resistance of the capillary tubing 6, it is also possible tocouple two or more capillaries with different diameters in series.

The cavity 5 in the interior of casing 1 in FIG. 1 is also equipped witha air venting conduit 12, the function of which is to equalize thepressure within the casing with the atmospheric pressure above thesampled liquid.

Upon installation of the preferred embodiment depicted in FIG. 1, thereis a hydraulic pressure gradient between the inlet of the solid phaseextraction cartridge 8, caused by the weight of the liquid column abovethe inlet and hereafter referred to as the head pressure, and the cavity5 at the interior of the casing 1, being in equilibrium with atmosphericpressure through air venting conduit 12 extending upwards above theupper surface of the liquid 2. The cartridge 8 and the capillary tubing6 will fill with the liquid 2 and the liquid 2 will enter the cavity 5interior of the casing 1. Until the cartridge 8 and capillary tubing 6are completely filled, there is a slight build up of backpressure sincethe liquid 2 flows upward and the increasing weight of the water columnin the cartridge 8 and the capillary tubing 6 contributes to theincreasing back pressure. To minimize the effect, the cartridge 8 can bepre-wetted before securing the cartridge 8 to the inlet conduit 7 andinstalling the sampler. The volume of the interior of the capillarytubing 6 is very small, typically less then 0.1 ml, in comparison to theinterior volume of the cavity 5 of the casing 1, which is typicallylarger than 100 ml, such as between 200 ml and 3 liters. Hence, thevarying back pressure only affects less than 0.1% of the sampled volumewhen the cartridge 8 is pre-wetted. When the cartridge 8 and capillarytubing 6 are completely filled, the cavity 5 of the casing 1 is filledin proportion to the pressure head above the sampler (FIG. 1B). As thisdevice is attached to a floating member 13 by means of a flexible wire14, the entire sampling unit will be hanging in the liquid 2 at constantdepth, even if the free liquid surface level is fluctuating.

Hence, the sampling rate of the liquid entering the casing will besubstantially constant in time until the liquid level in the casingreaches the level of the outlet 11 of the capillary tubing 6. Thepreferred installation time is usually known beforehand, and for thoseskilled in the art it will be possible to design a preferentialcombination of internal casing volume, capillary tubing 6 length anddiameter, the parameters that combined determine the optimal fluidsampling rate. From the above description it is clear that thispreferential combination will be different depending on the depth ofinstallation. In addition, this preferential combination will depend onthe viscosity of the sampled liquid 2, and therefore to a certain degreealso on the temperature of the adjacent liquid.

The mode of operation of the device as shown in FIG. 1, once assembledtowards beforehand known criteria, depth of installation and requiredinstallation time, is very easy. The sampler is installed at knowndepth; the sampler is passively filled at a predetermined rate, afterwhich the sampler is removed. The installation time will vary accordingto the aim of the sampling and may vary from, for example, one day up toseveral months. After removal of the sampler, the cartridge and thesampled fluid are analyzed for chemical or biological properties. Theanalysis of the cartridge 8 is described in detail in WO 03/098167.Briefly, the adsorbent 9 is extracted and analyzed for the mass ofchemical or biological compounds sorbed, and the cartridge 8 is analyzedfor the displaced amount of tracer substance 10. The liquid sampled inthe cavity 5 of the casing 1 may also be analyzed, both with respect tothe quantity (volume) and to the chemical constituents so as to deriveinformation on the chemical and/or biological concentrations of thesampled liquid.

According to other preferred embodiments of the invention, not shown inFIG. 1, more than one cartridge 8 may be fitted to the casing 1, Thesecartridges 8 may have similar adsorbents 9 and tracer compounds 10, inorder to quantify the precision and reproducibility of the samplingmethod. Alternatively, these different cartridges 8 may be equipped withdifferent adsorbent types 9 and/or tracer compounds 10 or differentamounts of tracer compounds 10. This is done to sample a wider range ofchemical or biological parameters.

According to another preferred embodiments of the invention, not shownin FIG. 1, the cartridge 8 or cartridges 8 may be arranged on the toppart of the casing 1, so that the flow of the liquid 2 through thecapillary tubing 6 is downward rather than upward. The benefit of thisposition is that it is possible to sample the liquid 2 closer to theliquid surface. The position of the cartridges 8 shown in FIG. 1prevents larger particles to settle on the inlet of the cartridge 8,which is a benefit when the liquid 2 contains high loads of suspendedparticles. According to another preferred embodiments of the invention,not shown in FIG. 1, the cartridge 8 or cartridges 8 may be positionedhorizontally on the vertical walls of the casing 1. This may be ofadvantage when the device is installed in shallow liquids, or when forother reasons it is considered important that there is no vertical flowthrough the cartridge 8, adding to the overall pressure gradient of theflow through the cartridge 8.

FIG. 2 shows another preferred embodiment of the sampling device,different from the one of FIG. 1 in that the internal pressure in thecavity 5 of the casing 1 is regulated by the air venting conduit 12which has an outlet 15 below the surface of the liquid 2 to obtain ahydrostatic pressure between the outlet 15 and the outlet 11 of thecapillary tubing 6 independent from the depth of the sampling device.This outlet 15 from the cavity 5 reduces the pressure gradient over theinlet of the sampler. When the sampler depicted in FIG. 2 is submergedin a liquid 2 and the capillary tubing 6 is filled with the liquid 2,the pressure gradient driving force that regulates the flow into thecavity 5 of the casing 1 is proportional to the head of the liquid 2above the outlet 11 of the capillary tubing 6, positioned in the topsection of the cavity 5 of the casing 1, minus the head of the liquidabove the outlet of the air-filled conduit 12. Hence, this pressuregradient is constant through the sampling period and independent of thedepth of installation with respect to the level of the liquid 2. Airwill be displaced from the cavity 5 through the outlet 15 while thecavity 5 is slowly filled at a constant rate defined by the abovedescribed constant pressure gradient. The pressure gradient in FIG. 2can be largely reduced compared to FIG. 1, and therefore wider capillarytubing 5 and/or coarser entrance filters with less hydraulic resistancemay be used. For those skilled in the art it will be possible to find apreferred combination of filter porosity, capillary length and diameter,to design the optimal fluid sampling rate for a given volume of thecavity 5 and desired installation time for the device. The mode ofoperation of the device shown in FIG. 2 is essentially the same as abovedescribed for the device shown in FIG. 1.

FIG. 3 shows a preferred mode of installation of the sampling device ofFIG. 1 in a groundwater well. Such wells are used for drinking waterproduction and for environmental purposes. The well is composed of asolid pipe section 16, the riser pipe, and a slotted section of the pipe17, also referred to as well screen. The later is in capillary contactwith the surrounding groundwater through narrow slots. The whole, orpart of, the well screen 17 is either permanently or intermittentlybelow the groundwater table. If the top of the well screen 17 is belowthe capillary fringe, the water in the pipe rises until the level in thepipe is in equilibrium with atmospheric pressure. In a non-confinedaquifer, the surrounding groundwater is also in equilibrium withatmospheric pressure. Hence, in this case the level in the standing pipeand the groundwater level will coincide. The water in the well screen 17is continuously replenished due to groundwater flow in the surroundingsediment, while the water above the well screen 17 is stagnant and notreplenished. The sampler is installed through a flexible wire 14 to thetop of the well pipe 16 by means of, for example, a stopper 18. Thesampler is installed such that the inlet of the cartridge 8 is levelwith the slotted section 17 of the pipe, so that the sampler is filledwith freshly replenished groundwater. Because the sampler here is fixedwith respect to the ground surface, the flow into the sampling devicewill fluctuate along with fluctuations in the water level in the pipe.This may be desirable, because the groundwater is, in the absence ofnearby surface water, proportional with the horizontal groundwater flux.Hence, in a non-confined aquifer the volume of the water displaced intothe sampling device can be used as a measure for the average groundwaterlevel during the installation period. In some cases, the rate ofgroundwater replenishment in the well is so low, that the water-qualityin the well is affected by diffusion of gases through the water in thestand-pipe. Therefore, it may be desirable to isolate the slottedsection 17 of the well from the riser pipe 16. For those skilled in theart it will be feasible to isolate these sections by the means ofpackers, for example as disclosed in U.S. Pat. No. 5,259,450 (Fischer).

One advantage of the methods and devices of the present invention isthat there is no need for power consuming functions, so that equipmentservicing is not needed in between two sampling events. The methods anddevices has further the advantage that it is suitable for sampling ofsolutes with very different chemical nature, both polar and apolarmolecules. A further advantage of the methods and devices is that theyare suited for sampling in liquids of very different chemical nature,such as water and aqueous solutions, but also apolar liquids such asoil, and organic solvents. A further advantage of the methods anddevices is that they may be applied to sample both free-dissolved andcolloidally-bound compounds. Another advantage of the methods anddevices is that the use of cartridges containing adsorbent media andtracer compounds can be easily stored before transportation to thelaboratory, unlike liquid samples that need conservation and rapidanalysis in the laboratory. A further advantage of the methods anddevices is that the sampling rate of the solutes is not dependent on thediffusion parameters, and the sampling method is suited for both low,medium, and high-flow environments. Also, an advantage of the methodsand devices is that the installation period is not dependent on themagnitude of the flux in the surrounding liquid. It is thereforepossible to design an optimal configuration of the device for a certainpre-determined installation time without a-priori knowledge of the flowconditions in which the device needs to be installed.

EXAMPLES

Experiments have been performed to document the feasibility ofcontrolling the sampling flow rate at different using atmosphericpressure compensation as shown in FIG. 1 and capillary inlet conduits 6.

As an example of the sampling flow rate of the sampling method used inshallow groundwater wells (1-7 m depth range), a sampler casing wasconstructed from a stainless steel cylinder (dimensions 22 mm OD×20 mmID×105 cm length), and Teflon top and bottom stoppers that were fittedto the cylinder by means of water tight flexible o-rings. The topstopper was constructed with fittings for nylon tubing (dimensions 3.18mm×1.9 mm×7 m length) and a 7 m flexible steel wire. The bottom stopperwas equipped with two external luer fittings and internal threadedfittings. The internal threaded fittings were fitted with a PEEK(polyetheretherketon) capillary (dimensions 1/16 inch×0.0025 inch×70 cmlength) extending vertically in the steel cylinder. Two 3 ml plasticcartridge with luer outlets were filled with an ion-exchange resin as amodel sorbent and calcium-citrate as a model tracer compound. The resinand tracer were fitted in the cartridge with polyethylene frits withpore size 20 μm. Two cartridges were pre-wetted and fitted to the bottomstopper, and the sampler was lowered in a 7 m standing pipe with 24 mminternal diameter, filled with tap water. The nylon tubing was kept incontact with atmospheric pressure above the standing pipe. In the depthinterval 1-7 m the sampler was positioned at six different depths for afixed period of time, after which the sampler was removed and volume ofthe accumulated water was determined. Flow rates were measured in therange of 0.01-0.25 ml/hr, depending on the depth of installation, seeFIG. 4. The relation of sampling rate with depth is linear withcorrelation coefficient R²=0.99, which is expected from capillary flowtheory.

The effective internal volume of the sampler is approximately 314 ml.With the sampler installed at a depth of 5 m below the water surface,the flow rate would be controlled to have a rate of 0.2 ml/hr, and withone cartridge fitted, the sampler casing would be filled after a periodof about 65 days. If a longer installation period is required, eitherthe volume of the casing should be increased, or the capillarydimensions should be changed to reduce the sampling rate.

As an example of the sampling method used in shallow surface water(0.3-2 m depth), two standard glass bottles were used as a samplercasings. The bottles were closed with a Teflon lid that was constructedwith water-tight fittings for nylon tubing (dimensions 3.18 mm×1.9 mm×2m length). The lid was further equipped with an external luer fittingand an internal threaded fitting. The internal threaded fitting was foreach of the two bottles fitted, in experiment 1, with PEEK capillaries(dimensions 1/16 inch×0.0025 inch×8 cm length), and, in experiment 2,with PEEK capillaries (dimensions 1/16 inch×0.004 inch×8 cm length). Two3 ml plastic cartridge with luer outlets were packed as described above,pre-wetted, and fitted to the luer fittings. Further, the lid wasequipped with the nylon tube extending to the bottom of the glassbottle. The two bottles were lowered in an upside-down position in awater reservoir and mounted on a support. The nylon tube was inequilibrium with the surrounding atmospheric pressure above thereservoir. In the depth interval 0.3-1.7 m the sampler was positioned atfive different depths in experiment 1, and at eight different depths inexperiment 2, for a fixed period of time. Then the sampler was removedand volume of the accumulated water was determined. In experiment 1, theflow rates were controlled in the range of 0.05-0.25 ml/hr, depending onthe depth of installation, see FIG. 5. In experiment 2 with the widercapillaries, the flow rates were controlled in the range of 0.2-1.5ml/hr, depending on the depth of installation, see FIG. 5. For bothcapillaries, the relation of sampling rate with depth was linear asexpected from capillary flow theory.

1. A method for determining chemical or biological properties of aliquid, comprising: situating a sampling device having a fluid-filledcavity at a subsurface position below an upper surface of the liquid,the fluid having a density lower than the liquid, allowing a flow of theliquid through a cartridge containing a material that interacts withcomponents of the liquid and into an inlet opening of the samplingdevice, said inlet opening is provided with a backpressure regulatingdevice so as to regulate a liquid inflow rate into the cavity for asampling period, said backpressure regulating device comprises acapillary tubing having an internal diameter of 10-500 μm simultaneouslyallowing a flow of the fluid out from the cavity through an outletopening of the sampling device, removing the sampling device from thesubsurface position for subsequent analysis for determining saidchemical or biological properties of the liquid, wherein the inletopening of the sampling device is connected to a liquid conduit havingits outlet inside the cavity and above a bottom of the cavity, so thatthe free surface of the liquid inside the cavity, during most of thesampling period is below the liquid conduit outlet, for the hydrostaticpressure driving the flow of the liquid into the cavity to besubstantially constant during most of the sampling period.
 2. A methodaccording to claim 1, wherein the fluid in the cavity is a gas.
 3. Amethod according to claim 1, wherein said sampling period is at leastone hour.
 4. A method according to claim 1, wherein the liquid inflowrate is within the range of 0.0001-5 Liters/day.
 5. A method accordingto claim 1, wherein said chemical or biological properties of the liquidare determined by analysis of the cartridge.
 6. A method according toclaim 1, wherein the cartridge contains at least one sorbent matrixbeing permeable to and insoluble by the liquid, the matrix comprising amaterial having sorbent properties for components of the liquid beingindicative for the chemical or biological properties thereof to bedetermined.
 7. A device for being situated at a subsurface position of aliquid in order to determine chemical or biological properties of theliquid, the device comprising a casing having an inner fluid-filledcavity, the fluid having a density lower than the liquid, an inletopening into the cavity provided with a backpressure regulating deviceso as to regulate liquid inflow rate into the cavity, said backpressureregulating device comprises a capillary tubing having an internaldiameter of 10-500 μm, a cartridge arranged so that the inflow passesthrough the cartridge containing a material that interacts withcomponents of the liquid so that said chemical or biological propertiesof the liquid may be determined by analysis of the cartridge, and anoutlet opening for allowing a flow of the fluid out from the cavity,wherein the inlet opening of the sampling device is connected to aliquid conduit having its outlet inside the cavity above a bottom of thecavity, so that the free surface of the liquid inside the cavity duringuse of the device is below the liquid conduit outlet for the hydrostaticpressure driving the flow of the liquid into the cavity to besubstantially constant.
 8. A device according to claim 7, wherein thefluid in the cavity is a gas.
 9. A device according to claim 7, whereinthe liquid inflow rate at use of the device is within the range of0.0001-5 Liters/day.
 10. A device according to claim 7, wherein thevolume inside the cavity below the level of the liquid conduit outletand the liquid inflow rate allow for a sampling period of at least onehour before the free surface of the liquid inside the cavity will reachthe level of the liquid conduit outlet.
 11. A device according to claim7, wherein the cartridge contains at least one sorbent matrix beingpermeable to and insoluble by the liquid, the matrix comprising amaterial having sorbent properties for components of the liquid beingindicative for the chemical or biological properties thereof to bedetermined.
 12. A device according to any one of claims 7 to 11, whereinthe sorbent matrix comprises at least one of: silica, aluminiumsilicate, aluminium zirconium, metal oxides, synthetic ion exchangeresins, carbonaceous materials, zeolites, carbohydrates and syntheticpolymeric materials.
 13. A device according to any one of claims 7 to11, wherein the cartridge further comprises at least one fluid permeablepartially soluble tracer material, which is released with controlledrate from the cartridge into fluids to be measured.
 14. A deviceaccording to claim 13, wherein the at least one tracer materialcomprises at least one of: inorganic, organic and hybridorganic/inorganic salts; organic, inorganic or hybrid organic/inorganicsolids, including polymers, copolymers, block copolymers and oligomersin which hydrolysis of certain bonds can lead to the loss of part of thematerial; and microencapsulated materials.
 15. A device according toclaim 14, wherein the tracer material is a salt having a solubilityproduct in the fluid in question of between 10⁻² and 10⁻⁶⁰.
 16. A deviceaccording to claim 14, wherein the tracer material is chosen from thefollowing group of salts: CaF₂, Ca-Citrate, CaHPO₄, Ca-oleate andCa-laurate.
 17. A method for determining chemical or biologicalproperties of a liquid, comprising: situating a sampling device having afluid-filled cavity at a subsurface position below an upper surface ofthe liquid, the fluid having a density lower than the liquid, allowing aflow of the liquid through an inlet opening of the sampling device saidinlet opening is provided with a backpressure regulating device so as toregulate the liquid inflow rate into the cavity for a sampling period,said backpressure regulating device comprises a capillary tubing havingan internal diameter of 10-500 μm, simultaneously allowing a flow of thefluid out from the cavity through an outlet opening of the samplingdevice, removing the sampling device from the subsurface position forsubsequent analysis for determining said chemical or biologicalproperties of the liquid, wherein the inflow passes through a cartridgecontaining at least one liquid permeable partially soluble tracermaterial, which is released with controlled rate from the cartridge intofluids to be measured, and a measure for the total liquid flow throughthe cartridge is obtained by analysing the remaining content of tracermaterial in the cartridge.
 18. A method according to claim 17, whereinthe at least one tracer material comprises at least one of: inorganic,organic and hybrid organic/inorganic salts; organic, inorganic or hybridorganic/inorganic solids, including polymers, copolymers, blockcopolymers and oligomers in which hydrolysis of certain bonds can leadto the loss of part of the material; and microencapsulated materials.19. A method according to claim 18, wherein the tracer material is asalt having a solubility product in the fluid in question of between10⁻² and 10⁻⁶⁰.
 20. A method according to claim 18, wherein the tracermaterial comprises at least one of: CaF₂, Ca-Citrate, CaHPO₄, Ca-oleateand Ca-laurate.
 21. A method according to claim 17, wherein thecartridge further contains a material that interacts with components ofthe liquid, and said chemical or biological properties of the liquid aredetermined by analysis of the cartridge.
 22. A method according to claim21, wherein said material comprises at least one sorbent matrix beingpermeable to and insoluble by the liquid, the matrix comprising amaterial having sorbent properties for components of the liquid beingindicative for the chemical or biological properties thereof to bedetermined.
 23. A method according to claim 17, wherein the inletopening of the sampling device is connected to a liquid conduit havingits outlet inside the cavity above the bottom of the cavity, so that thefree surface of the liquid inside the cavity during most of the samplingperiod is below the liquid conduit outlet for the hydrostatic pressuredriving the flow of the liquid into the cavity to be substantiallyconstant during most of the sampling period.
 24. A method according toclaim 17, wherein the fluid in the cavity is a gas.
 25. A methodaccording to any one of claims 17 to 24, wherein said sampling period isat least one hour, preferably within the range of 1 days to 400 days andmore preferred within the range of 14 days to 200 days.
 26. A methodaccording to claim 17, wherein the liquid inflow rate is within therange of 0.0001-5 Liters/day.
 27. A device for being situated at asubsurface position of a liquid in order to determine chemical orbiological properties of the liquid, the device comprising a casinghaving an inner fluid-filled cavity, the fluid having a density lowerthan the liquid, an inlet opening into the cavity provided with abackpressure regulating device so as to regulate the liquid inflow rateinto the cavity, said backpressure regulating device comprises acapillary tubing having an internal diameter of 10-500 μm, and an outletopening for allowing a flow of the fluid out from the cavity, wherein acartridge is arranged so that the inflow passes through the cartridgecontaining at least one fluid permeable partially soluble tracermaterial, which is released with controlled rate from the cartridge intofluids to be measured.
 28. A device according to claim 27, wherein thetracer material comprises at least one of: CaF₂, Ca-Citrate, CaHPO₄,Ca-oleate and Ca-laurate.
 29. A device according to claim 27, whereinthe inlet opening of the sampling device is connected to a liquidconduit having its outlet inside the cavity above the bottom of thecavity, so that the free surface of the liquid inside the cavity duringuse of the device is below the liquid conduit outlet for the hydrostaticpressure driving the flow of the liquid into the cavity to besubstantially constant.
 30. A device according to claim 27, wherein theliquid inflow rate at use of the device is within the range of 0.0001-1Liters/day.
 31. A device according to claim 27, wherein a volume insidethe cavity below the level of the liquid conduit outlet and the liquidinflow rate allow for a sampling period of at least one hour, preferablywithin the range of 1 days to 400 days before the free surface of theliquid inside the cavity will reach the level of the liquid conduitoutlet.
 32. A device according to claim 27, wherein the fluid in thecavity is a gas.
 33. A device according to claim 27, wherein the atleast one tracer material comprises at least one of: inorganic, organicand hybrid organic/inorganic salts; organic, inorganic or hybridorganic/inorganic solids, including polymers, copolymers, blockcopolymers and oligomers in which hydrolysis of certain bonds can leadto the loss of part of the material; and microencapsulated materials.34. A device according to claim 33, wherein the tracer material is asalt having a solubility product in the fluid in question of between10⁻² and 10⁻⁶⁰.
 35. A device according to claim 27, wherein thecartridge further comprises a material that interacts with components ofthe liquid so that said chemical or biological properties of the liquidmay be determined by analysis of the cartridge.
 36. A device accordingto claim 35, wherein said material contains at least one sorbent matrixbeing permeable to and insoluble by the liquid, the matrix comprising amaterial having sorbent properties for components of the liquid beingindicative for the chemical or biological properties thereof to bedetermined.
 37. A device according to claim 36, wherein the sorbentmatrix comprises at least one of: silica, aluminium silicate, aluminiumzirconium, metal oxides, synthetic ion exchange resins, carbonaceousmaterials, zeolites, carbohydrates and synthetic polymeric materials.